It's not complicated...start with a light frame and buy a few lighter weight parts...it goes something like this...
That's pretty impressive. In my case I bought a friend's almost new(ridden twice) Guru Sidero w/SRAM Rival and Ksyrium Elite wheels. Got it for $1200. I put a SRAM Red crankset and Red Yaw front derailleur on it but that's about it. I love this bike.